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This paper presents a method for the control design of five-level DCC converters based on mixed-integer optimization and machine learning. The resulting controller is computationally simple and can be easily implemented on low-resource control hardware using simple nested "if-else" statements. The optimization problem is recalled from previous work by modifying the cost function to further enhance the dynamic performance. Additionally, and in contrast to previous works, the online implementation accomplished in this paper allows the system to cover a wider range of operating points. For this, the optimization problem is solved offline for several operating conditions, and the results are gathered into a dataset to train classification and regression trees (CARTs), which are later used online. Due to the generalization capability of the CARTs, a more flexible and less resource-intensive implementation is achieved which is capable of operating at points outside the ones considered in the training dataset. The resulting control strategy is compared in simulation and experiments with several alternative approaches found in the literature. This approach can be extended to other power converter topologies, allowing the implementation of optimized modulations. • Modulation of five-level DCC as a mixed-integer optimization problem. • Achievement of wider range of operating points. • Classification and regression trees used for implementation of optimization problem. • Guidelines for robust implementation of such tress. • In-detail comparison with existing approaches both in simulation and experiments. [ABSTRACT FROM AUTHOR]

[Display omitted] • Small Ni 1−x Mn x Co 2 O 4 nanoparticles were synthesized by low-temperature gel combustion. • All the nanoparticles revealed strong catalytic performance in 4-nitrophenol reduction. • The catalytic performance of Ni 0.5 Mn 0.5 Co 2 O 4 nanoparticles was superior to NiCo 2 O 4 and MnCo 2 O 4 nanoparticles. • >90 % of 4-nitrophenol could be reduced in 12 min. • The anomalous catalytic behaviors of the nanostructures in repeated cycles were explained. Developing efficient catalysts is one of the challenging tasks for protecting our environment from contamination. Here we present the synthesis of Ni 1−x Mn x Co 2 O 4 , noble-metal free multimetallic oxide nanoparticles of 9.5–25.0 nm average sizes by a low-temperature gel combustion method and their utilization as catalysts for rapid reduction of 4-nitrophenol (4-NP) to aminophenol (AP). Scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and vibrating sample magnetometry were used for the characterization of the nanostructures. All the nanostructures revealed strong catalytic performance in the reduction of 4-NP, and the performance of Ni 0.5 Mn 0.5 Co 2 O 4 nanoparticles was superior (>90 % reduction in 12 min) to that of NiCo 2 O 4 and MnCo 2 O 4 nanoparticles. While the 4-NP reduction process followed a pseudo-first-order kinetics for all the catalysts, the reduction efficiency of the samples manifested a complex trend from cycle to cycle. The anomalous catalytic behavior of the nanostructures in 4-NP degradation has been explained. [ABSTRACT FROM AUTHOR]

Summary: Strontium (Sr) incorporated LaMnO3 (La0.7Sr0.3MnO3) nanoparticles have been synthesized by ball‐milling‐assisted solid‐state reaction to study their performance as electrode material for energy storage applications. The La0.7Sr0.3MnO3 nanoparticles exhibit superior electrochemical performance in neutral aqueous electrolyte (1 M Na2SO4) in comparison to LaMnO3 and SrMnO3 nanoparticles. This neutral electrolyte provides relatively higher ionic conductivity and viscosity compared to the ionic liquids and a wider potential window compared to the alkaline electrolytes. Electrochemical study of the electrodes prepared using La0.7Sr0.3MnO3 nanoparticles reveals pseudocapacitive behaviors with fast reversible Faradaic charge storage, which plays a key role in charge storage. The composite materials exhibit highest specific capacitance of 393.5 F g−1 at a scan rate of 2 mV s−1. Asymmetric supercapacitors fabricated using La0.7Sr0.3MnO3 nanoparticle and activated carbon operates over a wide potential window of 1.8 V, and it reveals high specific capacitance (197 F g−1) as well as high capacitive retention (87%) even after 4000 charge–discharge cycles. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach to deal with the regulation of the dc-link capacitor voltages and ac-side currents in a grid-connected five-level diode-clamped converter. Due to the controllability problems of this topology, guaranteeing a solid current control and, mainly, a correct dc-link voltage sharing, represents a complex technical challenge. With the purpose of coping with it, an averaged model that describes the system dynamics at both sides of the converter is presented, assuming that a modulation strategy is integrated in the system to generate the switching sequence. In order to derive the proposed model, no restriction concerning the use of only the three nearest vectors to the desired voltage reference is taken into account. Then, several changes of variables are carried out in the model equations to obtain control input decoupling for control purposes, while reducing the complexity of the model as well. Finally, the voltage and current controllers are designed separately using different control inputs in a straightforward way. Neither auxiliary hardware nor complicated mathematical calculations are required to achieve the control objectives. The effectiveness and good performance of the system under the proposed control approach are validated by simulation results, suggesting that the five-level diode-clamped converter can be a solid solution as an interfacing system connected to the utility grid for, e.g., industrial drives or renewable energy applications. [ABSTRACT FROM PUBLISHER]

[Display omitted] • Ge beyond x ∼ 0.4 in kesterite Cu 2 ZnSn 1-x Ge x S 4 causes the formation of secondary phases. • We could eliminate those secondary phases by an acid etching process. • The acid etching process does not affect the size and morphology of the nanostructures. • The phase pure kesterite films manifest high conductivity and enhanced hole concentration. Hole-transporting materials are very important for achieving high efficiency in perovskite solar cells. Thin films made of Cu 2 ZnSn 1-x Ge x S 4 have attracted the attention of researchers due to their potential as hole-transporting layers. However, defects and impurities define their effectiveness in solar cells. In this work, we present a facile wet chemical approach to remove the ZnS and Cu 8 GeS 6 impurities from small (∼11 nm) Cu 2 ZnSn 1-x Ge x S 4 (x = 0.0 to 0.7) nanoparticles synthesized by a hydrothermal process. The wet chemical process converted the nanostructures Cu-rich Zn-poor from their initial Zn-rich Cu-poor stoichiometry. Moreover, the bandgap energies of the nanostructures were reduced by about 0.1 eV after chemical treatment due to change the oxidation state of Cu from Cu1+ to Cu2+. The kesterite films prepared by spin coating of chemically treated nanoparticle inks revealed enhanced electrical conductivity and hole concentration in comparison to the films prepared using untreated nanoparticle inks. While the highest hole concentration of about 6.52x1018 cm−3 was obtained for the films made of Cu 2 ZnSn 1-x Ge x S 4 nanoparticles with the highest x value (x = 0.7), the highest hole mobility (18.9 cm2V−1s−1) was achieved for x = 0.3. The effects of secondary phase elimination on carrier concentration and mobility variation have been discussed. [ABSTRACT FROM AUTHOR]

Increased temperature and ocean acidification are two main factors threatening Arctic coastal ecosystems. To explore the consequences of increased average temperature and ocean acidification in Kongsfjorden, the performance of six common species of macroalgae, the chlorophyte Monostroma arcticum, the rhodophytes Phycodrys rubens, and Ptilota plumosa, and the phaeophytes Alaria esculenta, Desmarestia aculeata and Saccorhiza dermatodea, was tested after 9 days of culture at 4 and 10 °C in combination with current (ca. 390 ppmv) and future (1000 ppmv) levels of atmospheric CO under solar radiation in summer. Temperature affected mainly the photosynthetic performance as measured by PAM fluorescence, particularly the initial slope ( α) of ETR curves, the light saturation parameter ( E ), and F / F values, as well as the protein content, especially in the phaeophytes. On the other hand, CO affected mainly the internal accumulation of carbohydrates and lipids. The C:N balance was largely unaffected. External carbonic anhydrase activity was not inhibited at high CO, and nitrate reductase activity remained unaffected. The resulting growth rate was not altered by treatments in three out of the six species studied. On the other hand, P. rubens showed a positive effect of increasing temperature, D. aculeata was negatively influenced by CO, and S. dermatodea was positively affected by CO. Significant interactions between CO and temperature were found in 20 % of the analyses. Whether additive or synergistic, the co-occurrence of a higher temperature with other stressors such as elevated CO increases the probability of community changes by modifying the performance of these species. [ABSTRACT FROM AUTHOR]

The coccolithophore Emiliania huxleyi shows a variety of responses to ocean acidification (OA) and to high-CO2 concentrations, but there is still controversy on differentiating between these two factors when using different strains and culture methods. A heavily calcified type A strain isolated from the Norwegian Sea was selected and batch cultured in order to understand whether acclimation to OA was mediated mainly by CO2 or H+, and how it impacted cell growth performance, calcification, and physiological stress management. Emiliania huxleyi responded differently to each acidification method. CO2-enriched aeration (1200 µatm, pH 7.62) induced a negative effect on the cells when compared to acidification caused by decreasing pH alone (pH 7.60). The growth rates of the coccolithophore were more negatively affected by high pCO2 than by low pH without CO2 enrichment with respect to the control (400 µatm, pH 8.1). High CO2 also affected cell viability and promoted the accumulation of reactive oxygen species (ROS), which was not observed under low pH. This suggests a possible metabolic imbalance induced by high CO2 alone. In contrast, the affinity for carbon uptake was negatively affected by both low pH and high CO2. Photochemistry was only marginally affected by either acidification method when analysed by PAM fluorometry. The POC and PIC cellular quotas and the PIC:POC ratio shifted along the different phases of the cultures; consequently, calcification did not follow the same pattern observed in cell stress and growth performance. Specifically, acidification by HCl addition caused a higher proportion of severely deformed coccoliths, than CO2 enrichment. These results highlight the capacity of CO2 rather than acidification itself to generate metabolic stress, not reducing calcification. [ABSTRACT FROM AUTHOR]

The combined effects of ocean acidification and ultraviolet radiation (UVR) have been studied in the kelps Alaria esculenta and Saccharina latissima from Kongsfjorden (Svalbard), two major components of the Arctic macroalgal community, in order to assess their potential to thrive in a changing environment. Overall results revealed synergistic effects, however with a different amplitude in the respective species. Changes in growth, internal N, C:N ratio, pigments, optimum quantum yield (Fv/Fm) and electron transport rates (ETR) following CO 2 enrichment and/or UVR were generally more pronounced in S. latissima than in A. esculenta . The highest growth rates were recorded under simultaneous CO 2 enrichment and UVR in both species. UVR-mediated changes in pigment content were partially prevented under elevated CO 2 in both species. Similarly, UVR led to increased photosynthetic efficiency (α) and ETR only if CO 2 was not elevated in A. esculenta and even under high CO 2 in S. latissima . Increased CO 2 did not inhibit external carbonic anhydrase (eCA) activity in the short-term but in the mid-term, indicating a control through acclimation of photosynthesis rather than a direct inhibition of eCA by CO 2 . The higher benefit of simultaneous CO 2 enrichment and UVR for S. latissima respect to A. esculenta seems to involve higher C and N assimilation efficiency, as well as higher ETR, despite a more sensitive Fv/Fm. The differential responses shown by these two species indicate that ongoing ocean acidification and UVR could potentially change the dominance at lower depths (4–6 m), which will eventually drive changes at the community level in the Arctic coastal ecosystem. These results support an existing consideration of S. latissima as a winner species in the global change scenario. [ABSTRACT FROM AUTHOR]

SUMMARY This paper addresses the imbalance problem of the dc-link capacitor voltages in the three-level diode-clamped back-to-back power converter. In order to cope with it, a mathematical analysis of the capacitor voltage difference dynamics, based on a continuous model of the converter, is first carried out. It leads to an approximated model that contains explicitly several sinusoidal functions of time. In view of this result, the voltage imbalance phenomenon can be addressed as an output regulation problem, considering the sinusoidal functions of time as exogenous disturbances. Thus, a novel approach to deal with the mentioned problem in the back-to-back converter is presented. Then, the particular features of the disturbances are used to design several controllers. They all follow an asymptotic disturbance rejection approach. In this way, the estimates of the disturbances are used to apply a control law that cancels them while regulating the capacitor voltage balance as well. Finally, the performance of the proposed control laws is evaluated, presenting the simulation results obtained when the different controllers are implemented. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The effects of increased CO2 and irradiance on the physiological performance of the chlorophyte Dunaliella tertiolecta were studied at different PAR and UVR (UVA + UVB) irradiances, simulating the solar radiation at different depths, at present (390 ppmv, LC) and predicted CO2 levels for the year 2100 (1000 ppmv, HC). Elevated CO2 resulted in higher optimum and effective quantum yields (Fv/Fm and ΦPSII, respectively), electron transport rates (ETR) and specific growth rates (μ). Cell stress was alleviated in HC with respect to LC as evidenced by a decrease in reactive oxygen species (ROS) accumulation. DNA damage showed a 42-fold increase in cyclobutane-pyrimidine dimer (CPD) formation under the highest irradiance (1100 μmol quanta m−2 s−1) in LC with respect to the lowest irradiance (200 μmol quanta m−2 s−1). Photolyase (CII-PCD-PL) gene expression was upregulated under HC resulting in a drastic decrease in CPD accumulation to only 25% with respect to LC. Proliferating cell nuclear antigen (PCNA) accumulation was always higher in HC and the accumulation pattern indicated its involvement in repair or growth depending on the irradiance dose. The repressor of silencing (ROS1) was only marginally involved in the response, suggesting that photoreactivation was the most relevant mechanism to overcome UVR damage. Our results demonstrate that future scenarios of global change result in alleviation of irradiance stress by CO2-induced photoprotection in D. tertiolecta. [ABSTRACT FROM AUTHOR]

Abstract: This paper addresses the problems associated with the dc-link capacitor voltages of the three-level neutral-point-clamped power converter: the imbalance of the capacitor voltages as well as the presence of an ac-voltage low-frequency oscillation in the dc link of the converter. In order to cope with them, a mathematical analysis of the capacitor voltage difference dynamics, based on a direct average continuous model, is carried out, considering a singular perturbation approach. The analysis leads to a final expression where a sinusoidal disturbance appears explicitly. Consequently, the two problems can be handled together using the ordinary formulation of a problem of regulating the output of a system subject to sinusoidal disturbances, applying classical control theory to design the controller. In this way, the controller is designed including the disturbance estimate provided by a Luenberger observer to asymptotically cancel the disturbance, while also keeping the capacitor voltages balanced. Experiments for a synchronous three-level neutral-point-clamped converter prototype are carried out to evaluate the performance and usefulness of the converter working as a grid-connected inverter under the proposed control law. [Copyright &y& Elsevier]

[Display omitted] • Kesterite CZTS and CZTGS nanoparticles are synthesize by low-temperature hydrothermal process. • Substitution of 30% Sn by Ge in the kesterite lattice does not induce any impurity phase. • Ge incorporation in kesterite lattice increases the concentration of (V Cu + Zn Cu) defect complex. • Incorporation of Ge in kesterite lattice decreases [2Cu Zn + Sn Zn ] defect concentration. • Formation of V Cu enhances carrier concentration and conductivity of kesterite nanoparticles. Phase pure Cu 2 ZnSnS 4 (CZTS) and Cu 2 ZnSn 0.7 Ge 0.3 S 4 (CZTGS) kesterite nanoparticles of 10–35 nm size range were fabricated through a low-temperature hydrothermal process. Morphology, structure, and structural phase of the nanoparticles were determined utilizing field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and Raman spectroscopy. Electrical transport behaviors of the pelletized nanostructures were studied in a physical properties measurement system (PPMS) in the 100–320 K temperature range. Obtained results indicate that both the CZTS and CZTGS nanostructures have p-type conductivity, with high room temperature hole concentration and carrier mobility. Substitution of 30% Sn by Ge enhances the electrical conductivity of CZTS about four times. While the room temperature hole mobility in the kesterite nanostructures reduces to about 60%, the hole concentration increases about one order on Ge incorporation. The limited substitution of Sn atoms by Ge does not affect the position of acceptor levels in the electronic band gap of the kesterite nanostructures. However, it increases the concentration of Cu Zn and Zn Cu antisite defects and affects the transition temperature where the electrical transport of kesterite nanostructures changes from lattice scattering controlled to defect scattering controlled conduction. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a novel control strategy for a nonlinear boost inverter is proposed. The idea is based on generating an autonomous oscillator that does not need an external reference signal. This aim is achieved by using energy-shaping methodology with a suitable Hamiltonian function which defines the desired system behavior. A phase controller is added to the control law in order to achieve 180°-synchronization between both parts of the circuit as well as synchronize the voltage output with a pre-specified signal, e.g. synchronization with the electrical grid. An adaptive control is designed for dealing with the common problem of unknown load. In order to analyze the stability of the full system, singular perturbation approach is used. The resulting control is tested by means of simulations. [ABSTRACT FROM AUTHOR]

Twenty-one species of macroalgae (four Chlorophyta, eight Rhodophyta, and nine Phaeophyta) from the Kongsfjord (Norwegian Arctic) were examined for their response to nutrient enrichment (nitrate and phosphate) in the summer period. The enzymatic activities related to nutrient assimilation, external carbonic anhydrase (CAext, EC 4.2.1.1), nitrate reductase (NR, EC 1.6.6.1), and alkaline phosphatase (AP, EC 3.1.3.1), as well as the biochemical composition (total C and N, soluble carbohydrates, soluble proteins, and pigments) were measured. CAext activity was present in all species, and showed a general decrease after nutrient enrichment. Inversely, NR activity increased in most of the species examined. Changes in pigment ratios pointed to the implication of light harvesting system in the acclimation strategy. Despite enzymatic and pigmentary response, the Arctic seaweeds can be regarded as not being N-limited even in summer, as shown by the slight effect of nutrient enrichment on biochemical composition. The exception being the nitrophilic species Monostroma arcticum and, to a lesser extent, Acrosiphonia sp. For the rest of the species studied, changes in total internal C and N, soluble proteins, soluble carbohydrates, pigment content, and the internal pool of inorganic N were recorded only for particular species and no general pattern was shown. Acclimation to unexpected nutrient input seemed to ensure the maintenance of a stable biomass composition, rather than an optimized use of the newly available resource (except for the nitrophilic species). This indicates a high degree of resilience of the algal community to a disruption in the natural nutrient availability pattern. [ABSTRACT FROM PUBLISHER]

A fuzzy logic controller saturates outside the universe of discourse region. This saturation gives rise to a universal nonlinearity for this type of controller. In this paper, the effects of this nonlinearity are analyzed for the most usual fuzzy controllers: PD and PI fuzzy controllers. It is shown that due to this saturation some pathological behaviors such as oscillations or unstable limit cycles can occur. The methodology employed in the analysis is based on the describing function, which is determined for PD and PI fuzzy controllers. One example illustrates the relevance of the proposed methodology. [Copyright &y& Elsevier]

The carbon assimilation efficiency and the internal composition of the chlorophyte Dunaliella viridis have been studied under conditions of current (0.035%) and enriched (1%) levels of CO2, with and without N limitation (supplied as nitrate). Results show that both photosynthesis and growth rates are enhanced by high CO2, but the strategy of acclimation also involves the light harvesting machinery and the nutritional metabolism in an N supply dependent manner. D. viridis carried out a qualitative rather than a quantitative acclimation of the light harvesting system leading to increased PSII quantum yields. Total internal C decreased as a consequence of either active growth or organic carbon release to the external medium. The latter process allowed photosynthetic electron transport to proceed at higher rates than under normal CO2 conditions, and maintained the internal C:N balance in a narrow range (under N sufficiency). N limitation generally prevented the effects of high CO2, with some exceptions such as the photosynthetic O2 evolution rate. [ABSTRACT FROM AUTHOR]

Changes in the accumulation of cAMP levels were measured by the isotope dilution assay using protein kinase A in the lichen Evernia prunastri at varying light conditions. cAMP levels decreased following exposure to low irradiance (20 μmol quanta m−2 s−1, and below the compensation point for photosynthesis) of red light (600–710-nm wave length) and increased by 50% after far-red light illumination (15 μmol quanta m−2 s−1, 710–800-nm wavelength). Far-red partially reverted the effect of red light when the former was supplied after the latter. cAMP increased to its maximum level under high irradiance supplied by a non-photomorphogenic yellow light source (400 μmol quanta m−2 s−1, reaching photosynthetic saturation). The addition of small quantities of red and far-red light, however, had profound restricting effects on cAMP accumulation. The addition of inhibitors of electron transport chains did not promote any significant change in cAMP levels in any of the treatments, indicating that cAMP accumulation could not depend on ATP synthesis. We propose that the response of cAMP accumulation at low irradiance comprises the activation of a morphogenic pathway through a red/far-red photoreceptor. In addition, at high irradiance the response would occur most likely through photosystems II and I acting as sensors of light quantity, that can be strongly modified by the red/far-red photomorphogenic system. Thus, cAMP would be involved in sensing the overall light environment. [Copyright &y& Elsevier]

The appearance of self-sustained oscillations in high performance AC drives, and in particular, in induction motors whose speed is regulated with the industry standard field-oriented control, is a well-documented but little understood phenomenon. It is well known that the oscillations may be quenched by returning the outer-loop PI speed control, but no precise rules to carry out this task, which may be time consuming, are known. In this paper, we show that these oscillations may arise due to the existence of Hopf bifurcations. Some simple rules for selecting the gains of the PI controller are obtained as a result of our analysis. [Copyright &y& Elsevier]

Presents an application of the genetic programming paradigm to find the optimal policy of a large-scale 200-dimensional system. Genetic programming paradigm; Two kinds of functions used in genetic programming paradigm; Application of genetic programming paradigm to solve an optimal control problem of the MEREA3 model; Conclusions.

• Modulation of five-level DCC formulated as a mixed-integer optimization problem. • Optimization: Reduction on commutations number and balancing task fulfillment. • Off-line computation and look-up table implementation. • Guidelines for robust implementation of resulted look-up table. • Steady-state enhancement for distortion improvement. In power converters, the modulation stage commands the switching devices to drive the converter outputs to the voltage required by the inner controllers in order to achieve their objectives. However, in multilevel converters, the modulation may be in charge of an additional goal since it also has to tackle with the capacitor voltage balancing issue. This paper formulates the modulation of multilevel three-phase power converters, specifically five-level diode-clamped converters (DCC), as a mixed-integer linear optimization problem. In this paper, it is shown that the presented optimization problem can deal with the capacitor voltage balance at the same time that the number of commutations is minimized. The problem is solved offline and its solution is stored in a lookup table to be used during normal operation. Then, an online procedure to obtain the levels that modulate each phase from the lookup table is given. Comparisons with model predictive control, space-vector-based algorithms and other modulation approaches are presented in simulations. Several experimental results are presented showing the feasibility of this approach with changes in the operating conditions. [ABSTRACT FROM AUTHOR]

The article discusses various reports published within the issue, including one by R. A. Ynalvez and colleagues on two new carbonic anhydrases and another by S. Trimborn and colleagues on physiological characterisation of carbon concentrating mechanisms (CCMs) in the species of diatoms.

This paper presents an approach for dealing with the control of five-level, diode-clamped rectifiers. The control of such converters is challenging, as voltage balancing among capacitors is not a trivial task. Some of the existing approaches that cope with this problem use specific modifications of one of the traditional modulation techniques, such as using redundant vectors in space vector modulation (SVM). The main feature of the proposed technique is that part of the modulation is considered in the system equations and, in this way, the voltage balance can be solved designing a specific controller for this problem. As a result, several levels are used within a switching period. Furthermore, it is shown that the proposed approach hardly affects the control of active and reactive powers and total dc-link voltage in such a way that the well-known direct power control can be applied. As a consequence, the resultant modulation stage is simpler than other techniques based on, e.g., SVM. The effectiveness and good performance of the system under the proposed control approach are validated by both simulation and experimental results. [ABSTRACT FROM AUTHOR]

Despite the high productivity and ecological importance of seaweeds in polar coastal regions, little is known about their carbon utilization mechanisms, especially the kinetics of the CO2-fixing enzyme Rubisco. We analyzed Rubisco carboxylation kinetics at 4 °C and 25 °C in 12 diverse polar seaweed species (including cold-temperate populations of the same species) and the relationship with their ability to use bicarbonate, by using 13C isotope discrimination and pH drift experiments. We observed a large variation in Rubisco carboxylation kinetics among the selected species, although no correlation was found between either the Michaelis–Menten constant for CO2 (K c) or Rubisco content per total soluble protein ([Rubisco]/[TSP]) and the ability to use bicarbonate for non-green seaweeds. This study reports intraspecific Rubisco cold adaptation by means of either higher Rubisco carboxylation turnover rate (k catc) and carboxylase efficiency (k catc/ K c) at 4 °C or higher [Rubisco]/[TSP] in some of the analyzed species. Our data point to a widespread ability for photosynthetic bicarbonate usage among polar seaweeds, despite the higher affinity of Rubisco for CO2 and higher dissolved CO2 concentration in cold seawater. Moreover, the reported catalytic variation within form ID Rubisco might avert the canonical trade-off previously observed between K c and k catc for plant Rubiscos. [ABSTRACT FROM AUTHOR]

In this paper, a combination of a multi-layer quantum neural network (QNN) with the particle swarm optimization (PSO) algorithm is used with the aim of controlling a continuous stirred-tank reactor (CSTR) system. The CSTR process is highly non-linear and its dynamics are significantly sensitive to system parameter values. Normally, conventional controllers with fixed coefficients are applied to control this kind of system. In highly non-linear systems, having fixed controller coefficients in different operational conditions may decrease the performance of controllers. In the proposed scheme, by using a multi-layer QNN, an adaptive structure is designed for a PI-D controller. In order to train the QNN, the PSO algorithm is employed. With the aim of improving accuracy and convergence speed of the training process, some modifications have been applied to the movement of each particle towards the optimal point. Furthermore, in order to evaluate the performance of the system, the proposed scheme has been applied in various operational situations in the presence of disturbances and set-point change. The efficiency of the proposed control scheme is compared with PID and a perceptron neural network-based controller, and the simulation results endorse that the proposed scheme shows significantly better performance in different operating conditions. [ABSTRACT FROM AUTHOR]

This article proposes a sliding-mode-observer (SMO)-based control strategy to regulate the dc-link voltage for a three-phase two-level active front end (AFE). The SMO is designed for the voltage control loop to estimate the external load which is abruptly connected to the AFE dc-link and consequently causes the dc-link voltage fluctuation. The estimated load value is used to compensate the voltage loop controller, therefore, the voltage loop gains more robustness against the load perturbation and its disturbing effect is greatly reduced. The effectiveness and advantage of the proposed control strategy has been verified through theoretical analysis, simulations, and the real-application experiments conducted on a 5 KVA laboratory AFE. The results show that the proposed control strategy provides obvious improvement of the dc-link voltage control performance comparing with the conventional PI controller and demonstrates stronger robustness against the operating point variations caused by the changes in external load and dc-link capacitance. [ABSTRACT FROM AUTHOR]

Summary: This article focuses on the design of a robust switching control law for uncertain switched affine systems in the discrete‐time domain. More precisely, a novel control law is introduced whose parameters result from an optimization problem, aiming at reducing the volume of the attractive and invariant set, where the solutions to the closed‐loop system converge to. The design is based on a quadratic Lyapunov function and guarantees global practical stabilization, that is, global stabilization in a neighborhood of a desired operating point and robustness with respect to model uncertainties. Our method and the associated relaxed control law are then compared with existing conditions from the literature and are validated through numerical examples. [ABSTRACT FROM AUTHOR]

La 1-x Sr x MnO 3 perovskites are of enormous current interest due to their superior magnetoresistance and application as cathode material for solid oxide fuel cells. However, practical applications of these perovskites critically depend on size, composition, and concentration of La3+ vacancies at their surfaces. Here we present the fabrication of size controlled (90–255 nm average size), highly crystalline La 1-x Sr x MnO 3 (x = 0, 0.3, 0.5, and 1) nanoparticles, simply by ball-milling of metal acetylacetonate precursors in NaCl and subsequent air-annealing. The size of the nanoparticles increased in the order LaMnO 3+ δ < La 0.7 Sr 0.3 MnO 3 ≈ La 0.5 Sr 0.5 MnO 3 < SrMnO 3. While LaMnO 3+δ particles remain well dispersed, a fraction of particles containing Sr remains partially inter-connected after air-annealing (900 °C). A change in site symmetry of the Mn3+-O 6 octahedron promoted by the Jahn-Teller distortion of LaMnO 3+δ lattice was detected. Substitution of La3+ ions by Sr2+ increases the ferromagnetic interaction in La 1-x Sr x MnO 3 (x = 0, 0.3, 0.5) nanostructures, increasing their Curie temperature and magnetization (M s) progressively. Effect of particle dispersion due to Sr2+ incorporation on the lattice and magnetic behavior of the nanostructures is discussed considering the Jahn-Teller distortion and La3+ vacancy induced Mn3+ ion oxidation (to Mn4+) in the lattice. Image 1 • La 1-x Sr x MnO 3 perovskite nanoparticles of 90–255 nm av. Size range were fabricated by ball-milling. • Presence of Na+ ion at surface promotes the dispersion of LaMnO 3+δ nanoparticles. • Particle dispersion modifies the T irr of La 1-x Sr x MnO 3 nanostructures. • Substitution of La3+ by Sr2+ in La 1-x Sr x MnO 3 increases their T Curie and M s. • Jahn-Teller distortion and La3+ vacancy induced Mn3+ oxidation affect their magnetic behavior. [ABSTRACT FROM AUTHOR]

The article focuses on Radarnet-Sur first weather radar network in tropical high mountains. Weather radar networks deliver high-resolution spatiotemporal information, which could offer a viable solution to the problems. Despite their indispensable utility for weather forecasting and disaster prevention with regard to spatiotemporal rainfall assessments, radar networks are less developed in South America.

Ocean acidification and warming are affecting polar regions with particular intensity. Rocky shores of the Antarctic Peninsula are dominated by canopy-forming Desmarestiales. This study investigates the physiological and transcriptomic responses of the endemic macroalga Desmarestia anceps to a combination of different levels of temperature (2 and 7 °C), dissolved CO2 (380 and 1000 ppm), and irradiance (65 and 145 μmol photons m-2 s-1). Growth and photosynthesis increased at high CO2 conditions, and strongly decreased at 2 °C plus high irradiance, in comparison to the other treatments. Photoinhibition at 2 °C plus high irradiance was evidenced by the photochemical performance and intensive release of dissolved organic carbon. The highest number of differentially regulated transcripts was observed in thalli exposed to 2 °C plus high irradiance. Algal 13C isotopic discrimination values suggested an absence of down-regulation of carbon-concentrating mechanisms at high CO2. CO2 enrichment induced few transcriptomic changes. There was high and constitutive gene expression of many photochemical and inorganic carbon utilization components, which might be related to the strong adaptation of D. anceps to the Antarctic environment. These results suggest that increased temperature and CO2 will allow D. anceps to maintain its productivity while tolerating higher irradiances than at present conditions. [ABSTRACT FROM AUTHOR]

This article revisits the modeling of the grid-connected neutral point-clamped converter as a time-varying nonlinear hybrid dynamical system. As a result, an embedded control law that guarantees stability and fulfills the control objectives, namely dc-link voltage regulation, power-to-grid energy exchange and capacitor voltage balancing, is proposed. In addition, a rigorous study of stability is carried out without depending on an averaged model and considering the hybrid dynamical character of the system. Moreover, the hybrid control guarantees a minimum dwell time. This approach could be extended to other topologies or control laws in the search for rigorous stability guarantee The algorithm is evaluated and tested experimentally, verifying the feasibility of the approach. This process involves adapting the algorithm to be programmed in a FPGA as well as some further modifications to improve the steady-state performance. The experimental results are performed under several reference changes and perturbations to prove the feasibility of the proposed approach. [ABSTRACT FROM AUTHOR]

Ocean acidification affects with special intensity Arctic ecosystems, being marine photosynthetic organisms a primary target, although the consequences of this process in the carbon fluxes of Arctic algae are still unknown. The alteration of the cellular carbon balance due to physiological acclimation to an increased CO concentration (1300 ppm) in the common Arctic brown seaweeds Desmarestia aculeata and Alaria esculenta from Kongsfjorden (Svalbard) was analysed. Growth rate of D. aculeata was negatively affected by CO enrichment, while A. esculenta was positively affected, as a result of a different reorganization of the cellular carbon budget in both species. Desmarestia aculeata showed increased respiration, enhanced accumulation of storage biomolecules and elevated release of dissolved organic carbon, whereas A. esculenta showed decreased respiration and lower accumulation of storage biomolecules. Gross photosynthesis (measured both as O evolution and C fixation) was not affected in any of them, suggesting that photosynthesis was already saturated at normal CO conditions and did not participate in the acclimation response. However, electron transport rate changed in both species in opposite directions, indicating different energy requirements between treatments and species specificity. High CO levels also affected the N-metabolism, and C isotopic discrimination values from algal tissue pointed to a deactivation of carbon concentrating mechanisms. Since increased CO has the potential to modify physiological mechanisms in different ways in the species studied, it is expected that this may lead to changes in the Arctic seaweed community, which may propagate to the rest of the food web. [ABSTRACT FROM AUTHOR]

Abstract: Polar marine ecosystems have global ecological and economic importance because of their unique biodiversity and their major role in climate processes and commercial fisheries, among others. Portugal and Spain have been highly active in a wide range of disciplines in marine biology of the Antarctic and the Arctic. The main aim of this paper is to provide a synopsis of some of the results and initiatives undertaken by Portuguese and Spanish polar teams within the field of marine sciences, particularly on benthic and pelagic biodiversity (species diversity and abundance, including microbial, molecular, physiological and chemical mechanisms in polar organisms), conservation and ecology of top predators (particularly penguins, albatrosses and seals), and pollutants and evolution of marine organisms associated with major issues such as climate change, ocean acidification and UV radiation effects. Both countries have focused their polar research more in the Antarctic than in the Arctic. Portugal and Spain should encourage research groups to continue increasing their collaborations with other countries and develop multi-disciplinary research projects, as well as to maintain highly active memberships within major organizations, such as the Scientific Committee for Antarctic Research (SCAR), the International Arctic Science Council (IASC) and the Association of Polar Early Career Scientists (APECS), and in international research projects. [Copyright &y& Elsevier]

Multilevel converters are nowadays an enabling key in the integration of electric power into the grid as they introduce less distortion and, thus, they are more compliant with the grid standards, among other benefits. A well-known topology is the three-level Neutral-Point-Clamped whose control requires to deal with the capacitors voltage unbalance. This paper presents a modulation approach where the injection of a common component in the modulated voltage is studied in order to achieve such voltage balance. An optimization problem that, apart from the voltage balance, aims the lowest number of commutations and can be solved very efficiently with up to five computations of the cost function is formulated. The main advantages of the proposed modulation strategy are its simplicity and its flexibility, since it is also valid for unbalanced grid conditions and, with little added complexity, for low (and even zero) power factor conditions. Simulation results under unbalanced grid conditions are provided in order to show its validity under this scenario. The strategy is evaluated and compared with a space-vector-based approach in an experimental setup, yielding similar total harmonic current distortion, a 30% reduction in the number of commutations, and better voltage balance performance for lower power factor conditions. • A modulation approach for capacitors balance in NPC converters is proposed. • The advantages are simplicity and validity for unbalanced-grid-voltage conditions. • The number of commutations is optimized. • An enhancement is proposed to work under low-power-factor conditions. • Experimental comparison with virtual space vector is performed. [ABSTRACT FROM AUTHOR]

This paper uses a novel approach for the control of three-level neutral-point-clamped (NPC) rectifiers in order to tackle the capacitor voltage balance problem. A distinctive feature of the new control approach is that it is based on a model which is written in terms of the duty ratios for each phase at each level. Hence, the system model presents nine duty cycle variables. Despite the fact that this formulation is different from the usual ones, it is shown that the control problem of currents and dc-link voltage can be formulated in a similar way to conventional methods. Furthermore, the control of the capacitor voltage balance can be expressed by means of equations that are decoupled from the currents and dc-link voltage dynamics, which results in a specific controller for the voltage balancing that does not affect the previous dynamics. A key point of the proposed approach is that part of the modulation stage is implicit in the formulation. Two particular controllers are compared in this paper. The first one fulfills the different control objectives at the expense of a large number of commutations. This problem is overcome in a new proposed controller, which presents similar performance and a satisfactory number of commutations. Experimental results are performed showing the effectiveness compared with a modified virtual space vector modulation with capacitor voltage balance capabilities. [ABSTRACT FROM AUTHOR]